Process for manufacturing organic silazane polymers and process for manufacturing ceramics from the polymers

ABSTRACT

A process for manufacturing an organic silazane polymer which comprises reacting ammonia with a mixture of methyldichlorosilane, methyltrichlorosilane and dimethyldichlorosilane to obtain an ammonolysis product. The ammonolysis product is polymerized in the presence of a basic catalyst capable of deprotonation to obtain an organic silazane polymer. The silazane polymer may be further melted, shaped and infusibilized. The thus infusibilized product is finally sintered to obtain a ceramic material.

This is a division of application Ser. No. 903,409, filed Sept. 3, 1986now U.S. Pat. No. 4,771,118.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for manufacturing organic silazanepolymers which are suitably used as preceramic materials and also to aprocess for manufacturing ceramics from the organic silazane polymers.

2. Description of the Prior Art

Great interest has been currently shown in ceramics as materials whichhave good properties such as heat resistance, abrasion resistance,high-temperature strength and the like. However, because of the hardnessand brittleness, ceramics are very difficult to process. For themanufacture of shaped ceramic articles, it is accordingly general to usea method which comprises molding a fine powder of ceramic material intoa desired form such as by compression and sintering the molded article,or a precursor method in which an organic polymer, serving as apreceramic material, is melted or dissolved in a solvent, followed byprocessing the melted or dissolved polymer into a desired form andsintering it to render the polymer inorganic. The prominent feature ofthe precursor method resides in that ceramic products of such complexforms as will never be obtained in the sintering method for fine powdercan be obtained, i.e. products of specific forms such as fibers orsheets can be manufactured.

Among ceramics, SiC and Si₃ N₄ have attracted generally considerableattention because of the good characteristic properties thereof at hightemperatures, e.g. SiC has a high heat resistance and a high-temperaturestrength and Si₃ N₄ has a high thermal shock resistance and a highfracture toughness. Accordingly, there have been made various proposalson processes of producing SiC-Si₃ N₄ ceramics and also on processes ofproducing organic silicon precursors according to the precursor methodas is particularly shown (1) to (5) below. However, these proposedprocesses have still problems set forth below.

(1) In U.S. Pat. No. 3,853,567, there is disclosed a process ofobtaining SiC-Si₃ N₄ ceramics in which chlorosilanes and amines arereacted and subsequently heated at high temperatures to obtaincarbosilazanes, followed by subjecting the carbosilazanes to spinningand infusibilization and then sintering at high temperatures of from800° to 2000° C. However, this process requires high temperatures of520° to 650° C. in order to obtain the carbosilazane, thus being verydifficult to apply as an industrial process. In addition, thecarbosilazanes are disadvantageous in that the yield of ceramicmaterials therefrom is as low as about 55%. As will be apparent fromexamples of this U.S. patent specification, the chlorosilanes used areonly methyltrichlorosilane and dimethyldichlorosilane and the amine ismethylamine alone.

(2) U.S. Pat. No. 4,097,294 describes conversion of varioussilicon-containing polymers into ceramic materials by pyrolysis. Onlyone silazane polymer is set forth in this patent and the ceramic yieldis as low as 12% in a maximum. Although this U.S. patent specificationdescribes that ceramic materials may be formed into fibers or thinfilms, the formation is merely suggested as possible. In fact, there ismade little or no reference to moldability and processability ofpolymers which are considered to be most important in the precursormethod.

(3) There is known production of silazane polymers, for example, byreaction between chlorodisilanes and disilazanes in U.S. Pat. No.4,340,619, by reaction between chlorosilanes and disilazanes in U.S.Pat. No. 4,312,970, by reaction between chlorodisilanes and ammonia inU.S. Pat. No. 4,395,460, and by reaction between trichlorosilane anddisilazanes in U.S. Pat. No. 4,543,344. Moreover, silazane polymers areprepared by addition of metal halides to chlorosilanes and disilazanesas disclosed in U.S. Pat. No. 4,535,007 and by addition of metal halidesto chlorodisilanes and disilazanes as disclosed in U.S. Pat. No.4,482,689. It is stated in these references that all the silazanepolymers mentioned above may be converted to ceramic materials bypyrolysis. However, the ceramic yields of all the silazane polymers are,at most, 50 to 60 wt %. Similar to the U.S. Pat. No. 4,097,294, all theabove references do not describe in detail moldability andprocessability of the polymers, which are most important in theprecursor method. In particular, most references do not make mention ofceramic fibers in examples, or do not refer to strength of ceramicfibers in case where examples of ceramic fibers are shown. Only in U.S.Pat. No. 4,482,689, there is a description of strength, but ceramicfibers having such a low tensile strength as of 53 kg/mm² or 63 kg/mm²are obtained.

(4) In U.S. Pat. No. 4,482,669, there is described a process ofpreparing silazane polymers which comprises reacting ammonia with anorganic silicon compound of the formula, ##STR1## to obtain anammonolysis product and subjecting the product to condensation bydehydrogenation with alkali metal or alkalie earth metal hydrides toobtain silazane polymers. It is stated that the polymers obtained inthis process can be controlled in property depending on the degree ofcondensation by deprotonation and may take various forms of from oils tosolids having no definite melting points. However, when a polymer meltis molded or processed to prepare, for example, a continuous fiber bymelt spinning, it is necessary that the polymer have a certain degree ofpolymerization and be thermally stable. In the above process, thepolymer obtained will be in the form of a solid which has not a meltingpoint unless the polymerization is stopped on its way. In order toobtain a fusible polymer, the reaction time, reaction temperature,amounts of a catalyst and a solvent have to be controlled precisely butsuch a control may be very difficult and may not usually reproducible.The polymers obtained by the process are not thermally stable with thedisadvantage that gel-like substances are formed. In view of the abovetwo problems, this process may not be always considered to be suitableas an industrial process of manufacturing silazane polymers.

(5) Japanese Laid-open Patent Application No. 60-228489 describes aprocess of preparing a silazane polymer which comprises producing cyclicsilazane from a compound of the formula, CH₃, and monomethylamine,followed ##STR2## reacting the cyclic silazane with ammonia. In thispatent application, it is stated that the polymer is suitable as amaterial for chemical deposition, but physical properties of the polymerare not described in detail. The ceramic yield is not indicated at all.

As will be apparent from the foregoing description, hitherto proposedsilazane polymers, serving as preceramic materials, are not alwaysbeneficial for industrial production. In addition, these polymers werefound to be poor with respect to moldability and processability intoceramic fibers and like with a poor ceramic yield. Ceramic products,e.g. ceramic fibers, obtained from the known preceramic polysilazanematerials were found to have relatively poor physical properties such asstrength, modulus of elasticity and the like.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a processfor manufacturing preceramic materials which is adapted for industrialproduction and which enables one to produce the preceramic materialshaving good moldability and processability in high ceramic yield.

It is another object of the invention to provide a process formanufacturing ceramics composed of SiC-Si₃ N₄ of high quality from thepreceramic polymer materials.

In order to develop a process of manufacturing ceramic products whichmay belong to the art of a precursor method and also a process ofmanufacturing preceramic polymer materials which are suitable for themanufacture of the ceramic products and have good moldability andprocessability, our attention has been drawn to SiC-Si₃ N₄ ceramicswhich have good high-temperature characteristics of both SiC and Si₃ N₄.Accordingly, intensive studies have been made on the manufacture ofSiC-Si₃ N₄ ceramics according to a precursor method. As a result, it hasbeen found that silazane polymers having good thermal stability and acontrolled degree of polymerization can be obtained by mixing threechlorosilanes of methyldichlorosilane, methyltrichlorosilane anddimethyldichlorosilane, reacting the mixture with ammonia to obtain anammonolysis product, subjecting the ammonolysis product to condensationby dehydrogenation with a catalyst capable of deprotonation such as, forexample, an alkali metal or alkaline earth metal hydride, and completingthe condensation reaction. When the silazane polymers are melted,molded, heated in air or irradiated with an electron beam forinfusibilization, and sintered, ceramics of high quality composedpredominantly of SiC and Si₃ N₄ can be obtained. The present inventionis accomplished based on the above findings.

According to one embodiment of the present invention, there is provideda process for manufacturing organic silazane polymers which comprisesreacting a mixture of methyldichlorosilane, methyltrichlorosilane anddimethyldichlorosilane and ammonia to obtain an ammonolysis product, andpolymerizing the ammonolysis product in the presence of a basic catalystcapable of deprotonation. The present invention also provides an organicsilazane polymer obtained by the above process.

According to another embodiment of the invention, there is provided aprocess for manufacturing ceramics which comprises reacting a mixture ofmethyldichlorosilane, methyltrichlorosilane and dimethyldichlorosilaneand ammonia to obtain an ammonolysis product, polymerizing theammonolysis product in the presence of a basic catalyst capable ofdeprotonation to obtain an organic silazane polymer, melting, moldingand infusibilizing the organic silazane polymer, and sintering theinfusibilized polymer to obtain a ceramic material. There is alsoprovided a ceramic material composed of SiC-Si₃ N₄ obtained by the aboveprocess.

The above and other objects, features and advantages of the presentinvention will be more apparent from the following description.

DETAILED DESCRIPTION AND EMBODIMENTS OF THE INVENTION

In the process of manufacturing organic silazane polymers according tothe invention, three types of methylchlorosilanes, which aremethyldichlorosilane, methyltrichlorosilane and dimethyldichlorosilane,are used as one of the starting materials. After reaction between themixture and ammonia, a catalyst is acted only on the resulting productto complete the condensation by dehydrogenation, thereby obtaining anorganic silazane polymer of high quality having good moldability andprocessability in a high ceramic yield of, for example, 70 to 80%. Thisprocess does not require a precise or minute control of reaction time,reaction temperature, and amounts of catalyst and solvent and does notrequire troublesome operations of stopping the polymerization on itsway, thus ensuring industrial and easy manufacture of the silazanepolymer.

The process of manufacturing ceramics composed of SiC-Si₃ N₄ accordingto the invention uses the organic silazane polymer as a precursor orpreceramic material, from which ceramic products of a desired formhaving excellent physical properties can be readily obtained.

It will be noted that use of chlorosilanes as a starting material forpreparing silazane polymers or preceramic materials is conventionallyknown as set forth before. However, it has never been known heretoforethat the afore-indicated three chlorosilanes are selectively used incombination among a number of chlorosilanes and that after ammonolysisof the mixture, the resulting product is subjected to condensation bydehydrogenation in the presence of a specific type of catalyst to obtainsilazane polymers having such good characteristics as will never beenexperienced in prior art. These are first discovered by us.

The chlorosilanes used in the practice of the invention are acombination of methyldichlorosilane, methyltrichlorosilane anddimethyldichlorosilane, which are preferably used in amounts of from 55to 80 mole %, 10 to 30 mole % and from 5 to 25 mole %, respectively.When these chlorosilanes are used in combination, novel silazanepolymers are obtained. The silazane polymers have chemical structuresdifferent from a silazane polymer obtained from methyldichlorosilanealone as set forth in U.S. Pat. No. 4,482,669. More particularly, thesilazane polymers obtained according to the invention comprise differenttypes of repeating units in various bridges of these repeating units inthe structure. Since the silazane polymer having the novel structuredifferent from the known silazane polymer structure is used as thepreceramic material, the ceramic yield is remarkably improved over theyields of known processes of manufacturing ceramics according to theprecursor method. Moreover, the resultant ceramics have greatly improvedphysical properties such as tensile strength, modulus of elasticity andthe like.

As set forth before, the mixture of methyldichlorosilane,methyltrichlorosilane and dimethyldichlorosilane, used as one ofstarting materials for preparing organic silazane polymers according tothe invention, is preferred to have a composition of 55 to 80 mole % ofmethyldichlorosilane, from 10 to 30 mole % of methyltrichlorosilane, andfrom 5 to 25 mole % of dimethyldichlorosilane. Outside the abovecompositional ranges, the resulting polymers may become oily or may havea high melting point over 300° C. and is incapable of melting, thusbeing unfavorable.

The preparation of an ammonolysis product from the mixture of themethylchlorosilanes is not critical with respect to the procedure. Forinstance, there is conveniently used a process in which the mixture isreacted with gaseous NH₃ in organic solvents and, after removal of theammonium chloride byproduct, the organic solvent is stripped off.

In a subsequent step, the ammonolysis product is polymerized in thepresence of a basic catalyst capable of deprotonation. Preferably, theammonolysis product is subjected to condensation by dehydrogenation withthe catalyst in solvent to complete the reaction. The basic catalystcapable of deprotonation includes alkali metal or alkaline earth metalhydrides or metal amides such as KH, NaH, NaNH₂, KNH₂ and the like. Thesolvents used in the polymerization step may be ethers such as THF,dialkyl ethers and the like, aliphatic hydrocarbons such as pentane,hexane and the like, and aromatic hydrocarbons such as benzene, toluene,xylene and the like. Although the polymerization may usually be effectedat normal temperatures, the polymerization temperature should beappropriately selected from a range of 0° to 200° C., depending on thetype of solvent.

After completion of the condensation by dehydrogenation, the remainingbasic catalyst species is preferably decomposed with a nucleophiliccompound, such as methyl iodide. The resulting insoluble matter isremoved by filtration and the solvent is distilled off under reducedpressure. As a result, a silazane polymer having a melting point of from60° to 200° C. and an intrinsic viscosity of from 0.06 to 0.09 isobtained. The completion of the condensation reaction can be confirmedby stop of gas evolution.

The degree of polymerization and melting point of the silazane polymercan be suitably controlled by changing the mixing ratios of themethylchlorosilanes.

The organic silazane polymers obtained in this manner have highmoldability and processability and can be shaped, as preceramicmaterials, into suitable forms such as, for example, fibers or sheets.In addition, the polymers may be used as binder or adhesives.

In the process of manufacturing ceramics according to the invention, theorganic silazane polymers are melted, shaped or molded, infusibilizedand finally sintered. For this purpose, the polymer should preferablyhave a melting point of 60° to 200° C. and an intrinsic viscosity of0.06 to 0.09 as determined in benzene solution at 20° C. because suchpolymers permit easy melting and shaping.

The manners of melting, shaping and sintering of the organic silazanepolymers are not critical. The polymers are shaped or molded as desiredand sintered to obtain ceramic products of desired forms composed ofSiC-Si₃ N₄.

For instance, when ceramic fibers are fabricated, the organic silazanepolymer is heated to melt and spun by melting spinning. The spinningtemperature may vary depending on the melting point of the polymer, andis favorably in the range of from 100° to 300° C. Next, the thread-likematerial is infusibilized by heating in air or by irradiation with anelectron beam in vacuum or in an inert gas such as N₂ gas. In this step,the heating in air is preferably effected at a temperature of from 50°to 150° C. The electron beam irradiation is preferably at an exposeddose of from 50 to 200 Mrad. The thus infusibilized thread-like materialis sintered at high temperatures in a tension-free or tensionedcondition, thereby obtaining ceramic fibers composed mainly of SiC andSi₃ N₄ and having good strength and modulus of elasticity. The sinteringis preferably effected in vacuum or in an atmosphere of one or moregases, such as an inert gas including Ar, etc., N₂, H₂, NH₃ and thelike, at a temperature of from 700° to 2000° C., preferably from 700° to1500° C. The sintering under tension is more preferable, by which therecan be obtained ceramic fibers of high quality having a tensile strengthof from 200 to 300 kg/mm² and a modulus of elasticity of from 15 to 30tons/mm².

As will be apparent from the foregoing, the organic silazane polymerscan be conveniently produced according to the process of the invention.The silazane polymers are thermally stable and have a desired degree ofpolymerization with good moldability and processability. The polymerscan be manufactured in high ceramic yield and thus, are very suitablefor use as preceramic materials from ceramic fibers.

On the other hand, according to the process of manufacturing ceramics ofthe invention, ceramics of high quality composed mainly of SiC and Si₃N₄ can be obtained in high ceramic yield. Ceramic products of desiredforms such as ceramic fibers and sheets having high strength and highmodulus of elasticity can be obtained.

The present invention is more particularly described by way of examplesand comparative examples. The examples should not be construed aslimiting the present invention.

[EXAMPLE 1]

Ammonolysis step (1) usingmethyldichlorosilane:methyltrichlorosilane:dimethyldichlorosilane=75:15:10(mole %)

A dried, one liter four-necked flask equipped with an agitator, athermometer, an NH₃ gas inlet tube and dryice-methanol cooler wascharged with 850 ml of hexane, to which 43.1 g of methyldichlorosilane,11.2 g of methyltrichlorosilane and 6.5 g of dimethyldichlorosilane wereadded. followed by cooling down to -20° C. An excess of gaseous ammoniawas added to the solution at a rate of 12 liters/hour for 4 hours (atotal amount of added NH₃ of 2.1 mols). The reaction mixture was heatedto room temperature, whereupon a cooling device was changed to anair-cooling condenser in order to purge excess NH₃. Thereafter,byproduct ammonium chloride was removed from the reaction mixture byfiltration in a dry box. The resulting filter cake was washed with 200ml of hexane. The hexane was stripped off from the filtrate under areduced pressure of 1 mm Hg/60° C. The residue (ammonolysis product) wasa transparent fluid liquid and was obtained in an amount of 26 g.

Ammonolysis step (2) usingmethyldichlorosilane:methyltrichlorosilane:dimethyldichlorosilane=65:25:10(mole %)

850 ml of hexane was charged into a one liter four-necked flask havingthe same equipment as used above, to which 29.9 g ofmethyldichlorosilane, 14.9 g of methyltrichlorosilane and 5.2 g ofdimethyldichlorosilane were added, followed by cooling down to -20° C.Gaseous ammonia was added to the solution at a rate of 12 liters/hourfor 4 hours. Thereafter, the procedure of (1) was repeated, therebyobtaining 20 g of a transparent, fluid liquid (ammonolysis product).

Ammonolysis step (3) usingmethyldichlorosilane:methyltrichlorosilane:dimethyldichlorosilane=65:20:15(mole %)

A 2 liter four-necked flask having the same equipment as in (1) wascharged with 1500 ml of dehydrated hexane, to which 59.8 g ofmethyldichlorosilane, 23.9 g of methyltrichlorosilane and 15.5 g ofdimethyldichlorosilane were added, followed by reaction with gaseousammonia in the same manner as described above. Subsequently, the aboveprocedure of (1) was repeated, thereby obtaining 42 g of a transparentfluid liquid (ammonolysis product).

Polymerization step (1):

A 300 ml three-necked flask was equipped with an agitator, a thermometerand a dropping funnel, into which 0.2 g (5 mmols) of potassium hydrideand 125 ml of THF dehydrated with NaH were charged in a dry box. Theflask was removed from the dry box and connected to N₂ gas streamedtube. While the mixture was agitated at room temperatures to disperseKH, 10 g of the product obtained in the ammonolysis step (1) anddissolved in 75 ml of THF was gradually added from dropping funnel in 15minutes. During the addition, gases were evolved in large amounts and 1hour after the addition, the gas evolution was ceased. When 3 g ofmethyl iodide was added, a white precipitate of KI was formed. Afterfurther agitation for 30 minutes, most THF solvent was removed underreduced pressure and 80 ml of hexane was added to the residue. Themixture was filtered and the filtrate was subjected to removal of hexaneunder a reduced pressure (1 mm Hg) at 70° C., thereby obtaining 9.1 g ofa viscous solid (silazane polymer). This product had an intrinsicviscosity of 0.07 (benzene, 20° C.) and a melting point of 90° C. andwas soluble in organic solvents such as hexane, benzene, THF and thelike. The IR analysis revealed absorptions of NH at 3400 cm⁻¹, C--H at2980 cm⁻¹, Si--H at 2150 cm⁻¹, and SiCH₃ at 1260 cm⁻¹. The molecularweight by cryoscopic method using benzene was 1020.

Polymerization step (2):

10 g of the ammonolysis product obtained in the ammonolysis step (2) wasreacted with 0.2 g of KH in THF for 90 minutes in the same manner as inpolymerization step (1). After the gas evolution was ceased, CH₃ I wasadded, followed by repeating the procedure of polymerization step (1),thereby obtaining 9.3 g of a viscous solid (silazane polymer). Thepolymer had an intrinsic viscosity of 0.08 and a melting point of 120°C.

Polymerization step (3):

10 g of the ammonolysis product obtained in the ammonolysis step (3) wasreacted with 0.2 g of KH in THF for 90 minutes in the same manner as inpolymerization step (1). After the gas evolution was ceased, CH₃ I wasadded, followed by repeating the procedure of polymerization step (1),thereby obtaining 9.1 g of a viscous solid (silazane polymer). Thepolymer had an intrinsic viscosity of 0.07 and a melting point of 115°C.

Fiber preparation step (1):

30 g of the silazane polymer obtained in polymerization step (1) wasmelt spun at 130° C. by the use of a mono-hole melt spinning apparatus.The melt spinning was carried out very smoothly even after 4 hours andwas performed at a take-up speed of 400 m/minute. The resulting greenthread was subjected to infusibilization treatment by electron beamirradiation at 120 Mrad. Thereafter, the thread was sintered under aslight tension in a stream of N₂ at a heat-up rate of 100° C./hour at1100° C. for 30 minutes.

The ceramic yield was 75%. The resulting fiber has a diameter of 6micrometers, a tensile strength of 250 kg/mm² and a modulus ofelasticity of 25 tons/mm². The elementary analysis of the fiber revealedthat the fiber contained 58.3% of Si, 20.3% of C, 19.4% of N and 2% ofO, and was mainly composed of SiC-Si₃ N₄.

Fiber preparation step (2):

10 g of the silazane polymer obtained in polymerization step (2) wasspun at 160° C. by the use of such a melt spinning apparatus as used infiber preparation step (1). The spinning was carried out very smoothlyat a take-up speed of 420 m/minute. The resultant green thread wasthermally infusibilized under a light tension in air at 90° to 110° C.(5° C./hour). Thereafter, the thread was sintered in a tension-freecondition in a stream of N₂ at a heat-up speed of 100° C./hour at 1200°C. for 30minutes. The ceramic yield was found to be 80% and theresulting fiber had a diameter of 8 micrometers, a tensile strength of200 kg/mm² and a modulus of elasticity of 17 tons/mm². The elementaryanalysis of the fiber revealed that the fiber contained 56.2% of Si,19.2% of C, 15.4% of N and 9.2% of O, and was mainly composed of SiC-Si₃N₄.

Fiber preparation step (3):

20 g of the silazane polymer obtained in polymerization step (3) wasspun in a dry box by the use of such a melt spinning apparatus as usedin fiber preparation step (1) at 150° C. at a take-up speed of 450m/minute. The spinning was smoothly continued. The resulting greenthread was subjected to infusibilization in vacuum by irradiation of 90Mrad., by the use of an electron beam generator. Thereafter, theresulting fiber is sintered under tension in a steam of N₂ at 1250° C.(100° C./hour) for 30 minutes. The ceramic yield was found to be 77%.The fiber had a diameter of 6 micrometers, a tensile strength so 260kg/mm² and a modulus of elasticity of 23 tons/mm².

[COMPARATIVE EXAMPLE]

Ammonolysis step:

A one liter four-necked flask equipped with an agitator, a thermometer,an NH₃ gas inlet tube and a dryice-methanol cooler was charged with 850ml of dehydrated hexane, to which 46 g of methyldichlorosilane wasadded. Gaseous ammonia was introduced into the solution for reaction ata rate of 12 liters/hour for 3.5 hours. Thereafter, the ammonolysis step(1) of Example was repeated, thereby obtaining 20 g (85% ) of atransparent fluid liquid.

Polymerization step:

After charging 0.2 g of KH and 125 ml of THF into a 300 ml three-neckedflask and agitating to disperse KH in THF, a mixture of 75 ml of THF and10 g of the transparent fluid liquid obtained above was dropped into thedispersion from a dropping funnel at room temperatures in 15 minutes.Agitation was continued for thirty minutes after completion of thedropping, and then 2 g of CH₃ I was added to stop the reaction on itsway. Subsequently, the procedure of polymerization step (1) of Examplewas repeated, thereby obtaining 9.0 g of a viscous solid. This solidmaterial had an intrinsic viscosity of 0.06 and a melting point of 75°C. The polymerization in this system was controlled with respect to thetemperatures, amount of the catalyst, and polymerization time in orderto keep a constant degree of polymerization. However, reproducibleresults could not be obtained.

Fiber preparation step:

8 g of the resulting silazane polymer was charged into a mono-hole(nozzle diameter: 0.5 mm) melt spinning apparatus and melt spun at 110°C. Initially, discharge from the nozzle was good and the spinning waspossible. Thirty minutes after commencement, discharge from the nozzlestopped. Although the temperature gradually increased, no discharge tookplace. After cooling, the polymer was removed and its melting point wasmeasured. As a result, it was found that the polymer did not melt evenat 300° C. and was insoluble in various solvents. The green threadinitially obtained was subjected to irradiation with an electron beam at90 Mrad., followed by sintering in a stream of N₂ at a heat-up speed of100° C./hour at 1100° C. for 30 minutes. The ceramic yield was found tobe 58%. The resulting fiber had a diameter of 7 micrometers, a tensilestrength of 50 kg/mm² and a modulus of elasticity of 5 tons/mm², thusbeing poorer than in the case of the invention.

What is claimed is:
 1. A process for manufacturing a ceramic materialwhich comprises reacting ammonia with a mixture of methyldichlorosilane,methyltrichlorosilane and dimethyldichlorosilane to obtain anammonolysisproduct, and polymerizing the ammonolysis product in the presence of abasic catalyst capable of deprotonation to obtain an organic silazanepolymer, melting, molding and infusibilizing the silazane polymer, andsintering the resulting polymer to obtain a ceramic material.
 2. Aprocess according to claim 1, wherein mixing ratios ofmethyldichlorosilane, methyltrichlorosilane and dimethyldichlorosilaneare in ranges of 55 to 80 mole %, 10 to 30 mole % and 5 to 25 mole %,respectively.
 3. A process according to claim 1, wherein said organicsilazane polymer has a melting point of 60° to 200° C. and an intrinsicviscosity of 0.06 to 0.09 as determined in benzene at 20° C.
 4. Aprocess according to claim 1, wherein said organic silizane polymer isinfusibilized in air at a temperature of from 50° to 150° C.
 5. Aprocess according to claim 1, wherein said organic silazane polymer isinfusibilized in vacuum or in N₂ gas by irradiation of an electron beamat an exposed dose of from 50 to 200 Mrad.
 6. A process according toclaim 1, wherein said organic silazane polymer is melted and spun toobtain ceramic fibers.
 7. A process according to claim 1, wherein thesintering is effected at a temperature of from 700° to 2000° C.
 8. Aprocess according to claim 7, wherein the sintering is effected invacuum or in an atmosphere of at least one gas selected from the groupconsisting of inert gases, N₂, H₂ and NH₃ gases.
 9. The process of claim1 wherein said basic catalyst is KH, NaH, NaNH₂, or KNH₂.
 10. Theprocess of claim 1 wherein the ammonolysis reaction is effected in aninert solvent.
 11. The process of claim 1 wherein the polymerizationreaction is effected in an inert solvent at a temperature of from 0° to200° C.
 12. The process of claim 1 further comprising adding anelectrophilic compound after completion of the polymerization reactionwhereby the remaining basic catalyst is decomposed.
 13. The process ofclaim 1 wherein the basic catalyst is selected from the group consistingof alkali metal hydrides, alkaline earth metal hydrides, alkali metalamides and alkaline earth metal amides.